1. Field of the Invention
The present invention relates to a backlight unit, and in particular to a backlight unit for a display device having a main screen and a sub screen. The backlight unit drives light-emitting diodes corresponding to the sub screen utilizing an independent circuit, thereby reducing current consumption.
2. Description of the Related Art
Liquid crystal displays (LCDs) are employed applied in variety of electronic devices, such as mobile phones, digital cameras, personal digital assistants, and other devices used in environments providing varying degrees of brightness. In order to provide adequate display brightness, backlight sources are provided located in an rear of the LCD panel.
Currently, many mobile phones have hinged displays with a main screen and a sub screen disposed on eacg side thereof. The main screen is disposed on the inner side of the hinged display and displays a main menu and related information. The sub-screen is disposed on the outer side of the hinged display and displays general information, such as data, time and so on. Generally, the main screen and the sub screen respectively have a light source and a light guide configured in a backlight unit within a liquid crystal module of the mobile phone. The described mobile phone suffer from the disadvantages of large volume and excessive power consumption.
To solve the described problems, light-emitting diodes (LEDs) coupled in series and one light guide are employed in a backlight unit for displaying images in the main screen and the sub screen. FIG. 1 shows a schematic diagram of the backlight unit with serial light-emitting diodes. A main screen MD1 and a sub screen SD1 are relatively disposed. LEDs 1A to 1D correspond to the main screen MD1 and LEDs 1B and 1C further correspond to the sub screen SD1. When the main screen MD1 or the sub screen SD1 is used, all LEDs 1A to 1D are driven to emit light. That is, the LEDs corresponding to the main screen MD1 and the LEDs corresponding to the sub screen SD1 are all lit.
Practically, when the mobile phone is in standby mode, the hinged cover is closed such that the sub screen SD1 on the outer side of the flip cover can be viewed. Meanwhile, the LEDs 1B and 1C corresponding to both screens MD1 and SD1, and LEDs 1A and 1D corresponding to the main screen MD1 are all driven to emit light. The lit LEDs 1A and 1D cause unnecessary power consumption and reduced battery life.
Additionally, LEDs 2A to 2D coupled in parallel are applied in a backlight unit, as shown in FIG. 2. Because the impedances of LEDs 2A to 2D are different, brightness thereof is unequal, resulting in uneven brightness of the backlight unit and poor display quality.